Self-destructing metal structures

ABSTRACT

A metal laminate is provided which will deteriorate after the interior of the laminate is contacted by moisture. Selfdestructing containers are fabricated of this structural laminate. The laminate includes at least two layers of dissimilar metals which are electronically connected. One of the metal layers is an aluminum-based metal and the other layer is a metal anodic to the aluminum-based metal, such as a magnesium-based metal. Positioned between the metal layers is at least one layer of an electrolyte-forming composition capable of establishing ionic communication between the metal layers when the composition is contacted with moisture. A preferred electrolyte-forming composition is an inorganic salt containing an alkali metal or an alkaline earth metal, such as sodium chloride. When the electrolyte-forming composition is contacted by sufficient moisture to provide ionic conduction between the metal layers, a galvanic cell is formed having the unique property of simultaneously deteriorating at both the anode and cathode.

United States Patent [72] Inventor Percy F. George Midland, Mich.

[21] Appl. No. 4,613

[22] Filed Jan. 21, 1970 [45] Patented Dec. 21, 1971 [73] Assignee TheDow Chemical Company Midland, Mich.

[54] SELF-DESTRUCTING METAL STRUCTURES 12 Claims, 2 Drawing Figs.

[52] U.S.Cl 204/197, 29/195, 29/197, 29/197.5,136/114,136/166,

[51] Int. Cl ..B65d 25/14, B65d 7/42 [50] Field ofSearch 29/183, 191,195, 196, 1962-1966, 197, 197.5; 136/114, l66,167;204/147,148,196,197,141;220/1 BC,

Primary Examiner-Ta-Hsung Tung At!0rneys-Griswold & Burdick, V. DeanClausen and William R. Norris ABSTRACT: A metal laminate is providedwhich will deteriorate after the interior of the laminate is contactedby moisture. Self-destructing containers are fabricated of thisstructural laminate. The laminate includes at least two layers ofdissimilar metals which are electronically connected. One of the metallayers is an aluminum-based metal and the other layer is a metal anodicto the aluminum-based metal, such as a magnesium-based metal. Positionedbetween the metal layers is at least one layer of an electrolyte-formingcomposition capable of establishing ionic communication between themetal layers when the composition is contacted with moisture. Apreferred electrolyte-forming composition is an inorganic saltcontaining an alkali metal or an alkaline earth metal, such as sodiumchloride. When the electrolyte-forming composition is contacted bysufficient moisture to provide ionic conduction between the metallayers, a galvanic cell is formed having the unique property ofsimultaneously deteriorating at both the anode and cathode.

mcmzn new ml $62 909 1 INVENTOR. Percy E Geo/9e SELF-DESTRUCTING METALSTRUCTURES BACKGROUND OF THE INVENTION The invention relates broadly toself-destructing metal structures comprising two or more electronicallyconnected layers of dissimilar metals and one or more layers of anelectrolyte-forming composition positioned between each pair of metallayers. The invention further concerns a metal container fabricated ofsuch a structural laminate.

Most nonreturnable metal containers in use today require a relativelylong period of time to deteriorate when the container is discarded. Withmillions of such containers being discarded each day, the problem ofsufficient space to dispose of the refuse is one of growing concern. Itwould be desirable, therefore, to provide a metal container which afterbeing opened would deteriorate within a few months in an outdoorenvironment.

OBJECTS Accordingly, a principal object of the invention is to provide ametal laminate suitable for the fabrication of containers, which afterbeing opened will deteriorate substantially more rapidly than the priormetal containers.

A more specific object is to provide a metal container fabricated from alaminate including dissimilar metal layers and an electrolyte-formingcomposition, to provide a container which will undergo deteriorationaided by galvanic corrosion upon contacting the electrolyte-formingcomposition with moisture.

Still another object is to provide a structural laminate in which eachof the metal components of the laminate deteriorates simultaneously.

SUMMARY OF THE INVENTION Broadly, the invention provides a structuralmetal laminate useful for the fabrication of metal containers, whichlaminates undergo simultaneous deterioration in each of its metalcomponents, once its interior is contacted by moisture. In one furtherembodiment of the invention, a container is provided, with at least onewall member of the container comprising the delineated structurallaminate. This laminate includes at least two layers of dissimilarmetals, with the metal layers being electronically connected, i.e.,connected so as to permit electron flow from one to the other. One ofthe metal layers is an aluminum-based metal and the other layer is ametal anodic to the aluminum-based metal. At least one layer of anelectrolyte-forming composition containing an alkali metal or analkaline earth metal salt is positioned between the metal layers of thelaminate, the composition being capable, when connected with moisture,of providing ionic communication between the metal layers.

FIG. 1 is a front elevation view, partly in section, of a container madefrom the described laminate.

FIG. 2 is a view of the container of FIG. 1 taken on the lineDESCRIPTION OF A PREFERRED EMBODIMENT Referring to the drawings thenumeral indicates generally a cylindrical metal container. Basically,container 10 comprises a sidewall 11, a top wall 12 and a bottom wall13. According to the embodiment of the invention illustrated, thecontainer walls comprise a three-layer structural laminate. The laminateincludes at least two metal layers l4, 15, with one layer being analuminum-based metal and the other layer being a metal anodic to thealuminum-based metal layer. Electron flow between the metal layers l4,15 is provided for by electronically connecting the layers byface-to-face contact 16 of the two metals within the top and bottomchime portions 17, 17a of container 10. A similar electronic connectionbetween the metal layers of the laminate which comprise the sidewall 11is formed by joint 18 of side seam .9 (note FIG. 2). At least one layerof an electrolyte-forming composition 20 is positioned between the metallayers 14 and 15.

The metal layers l4, 15 of the laminate structure may be either singlemetals, metal alloys or clad metals so long as one layer is essentiallyan aluminum-based metal and the other metal layer is anodic to thealuminum-based metal layer. For the aluminum-based metal layer, it ispreferred to use an aluminum alloy containing at least 50 percentaluminum, and more preferably at least about 85 percent aluminum.Typical aluminum alloys which may be used are those compositions listedin the Registration Record of Aluminum Association Alloy Designationsand Chemical Composition Limits for Wrought Aluminum Alloys.Representative of the alloy compositions which may be used are thosedesignated by the following Aluminum Association numbers: ll00, 2017,3002, 4045,5052, 5056, 6061, 7075 and 800l.

Selection of an appropriate metal or metal alloy which will be anodic tothe aluminum-based metal AZ6IA, be determined from a standard referencetable of the Electromotive Series of Metals and Alloys (see LangesHandbook of Chemistry, 10th ed., edited by N. A. Lange, McGraw-Hill BookCo., I967, pp. 1,223-l,230). In the practice of the invention thepreferred anodic metal layer is a magnesiumbased alloy, which containsat least 50 percent magnesium and preferably at least about 85 percentmagnesium. Typical magnesium alloy compositions which may be usedinclude those listed by Amer. Soc. for Testing Materials under thefollowing ASTM designations: MIA, AZ3lB, A3A, AZ61A, AZ6lB, AZA, ZK60Aand ZEIOA (see Metals Handbook, Amer. Soc. for Metals). Representativeof other metals or alloys which may be used as the anodic metal layerare zinc-based metals and galvanized steel.

The choice of which metals or alloys (15) employed for each of thelayers in the container laminate will depend on various factors, such asstrength requirements of the container laminate, cost and feasibility ofusing certain metals in a container fabrication and the like. Althoughthe thickness of the individual metal layers utilized is not critical,they will usually be metal foils less than about %-inch thick. Anotherconsideration is positioning of the metal layers within a fabricatedcontainer. For example, if it is desired to have the inner layer (14)function as a cathode and the outer layer 15 function as an anode, theinner layer will be an aluminum-based metal and the outer layer will bea metal anodic to the aluminum-based layer, such as a magnesium-basedalloy. If it is desired instead that the inner layer be anodic and theouter layer be cathodic, the positions of the aluminum-based andmagnesium-based metal layers in the laminate are reversed. Preferably,the container laminate, which includes the metal layers l4, l5 and theelectrolyte-forming composition 20, is a generally flexible structurehaving an overall or total thickness of not more than about 0.250 in.

For the electrolyte-forming composition 20, the preferred materials arethose dry salts or mixtures of salts which are capable of ionizing in awater solution to thereby provide ionic communication between themetallayers l4, 15, but which in a dry condition are essentiallynonconductors. Broadly, the invention includes the anhydrous alkalimetal and alkaline earth metal salts. The alkali metal salts arepreferred. Especially preferred are the alkali metal salts of strongacids, such as sodium chloride, potassium chloride, lithium chloride andsodium sulfate. The preferred alkaline earth metal salts are the saltsof magnesium and barium, particularly barium chloride and magnesiumchloride. In the practice of the invention, one or more hygroscopicmaterials may be added to the electrolyte-forming salt to enhance itswater-absorbing capacity. Particularly preferred electrolyte-formingcompositions are mixtures of alkali metal salts with hygroscopic ordeliquescent salts, such as calcium chloride or magnesium chloride.

Positioning or layering of the electrolyte-forming salt between themetal layers of the laminate structure may take several forms. Forexample, the salt composition may be adhered to the inner surfaces ofthe metal layers, it may be placed between the metal layers as a loosecomposition or it may be impregnated onto a bibulous carrier materialand the carrier strip sandwiched between the metal layers of thelaminate. Use of a salt-impregnated carrier strip as theelectrolyte-forming composition is preferred, since the bibulous carriermaterial can act as a wick to help carry moisture between the metallayers of the laminate after the container is opened. Suitable carriermaterials for the electrolyte-forming composition include absorbentpapers, such as paper toweling; porous hydrophilic adhesives, porouspolymeric films, such as open-cell plastic films, and soluble polymericfilms or water-soluble cellulosic film formers, such as methylcellulose,hydroxyethyl cellulose and carboxymethylcellulose. It will be readilyunderstood that the electrolyte-forming composition is sealed betweenthe metal layers of the laminate to insure that the composition does notcome into premature contact with moisture.

When it is desired to initiate deterioration of the laminate, as in thewalls ofa discarded container, the laminate structure is severed, aswith a tear strip (not shown) integrally formed in the top wall 12 ofthe container. Although a tear strip is preferred, any device which willeffectively sever or puncture the container laminate, such as a canopener, may be used to achieve communication between theelectrolyte-forming composition and environmental moisture. When thecontainer laminate is severed and the electrolyte-forming salt is wettedwith moisture, which may be in the form of rain, snow, dew, condensate,atmospheric moisture, or the like, an electrolyte solution is formed,providing ionic communication between the metal layers. ln the practiceof the invention, the formation of the electrolyte solution initiates asimultaneous deterioration of the anodic and cathodic metal layers ofthe container laminate. Although not fully understood, thisdeterioration is at least in part a result of galvanic action.

In the illustrated container, once the laminate structure of the topwall 12 is severed, wetting of the salt layer 20 in sidewall 11 of thecontainer is enhanced by migration of the moisture through one or moreperforations 21, which extend through the double metal layerjoint formedin chime portions 17 and 17a. ln fabricating the chime portion 17 itwill be apparent that the perforations 21 must be placed far enough upin the double layer joint to be sealed off from the contents of thecontainer. Construction of the chime portion in this manner will preventany moisture in the container contents from contacting theelectrolyte-forming salt before the container is opened and therebyavoid premature initiation of the corrosive reaction.

Further embodiments of the invention include laminates and containersfabricated thereof, comprising a multilayer, structural laminate withmore than two metal layers and one or more electrolyte-formingcompositions positioned between each pair of metal layers. A specificexample of this embodiment is a structural laminate comprising twolayers of an aluminum-based metal and one layer of a magnesium-basedmetal, which is positioned between the aluminum layers. The laminatealso includes an electrolyte-forming composition, defined by a bibulouscarrier strip impregnated with sodium chloride, which is positionedbetween each of the pairs of metal layers.

The following examples are given to illustrate the invention, but arenot to be construed as limiting the invention to the embodimentdescribed herein.

EXAMPLE 1 A sheet of paper towel measuring approximately 4 sq. in. wassoaked in a saturated aqueous solution of sodium chloride and the saltimpregnated paper sheet was dried at room temperature. A sheet ofmagnesium alloy (AZ6IB) measuring about 4 in. square and 0.003 in. thickwas adhered to one side of the paper sheet by applying spots of adhesiveat various places between the metal and the paper. To the opposite sideof the paper sheet was adhered a sheet of aluminum foil about 4 in.square and 0.002 in. thick, to complete the three-layer laminate. Thelaminate was cut into two separate sections. The top edge of eachsection was folded over to form an electronic connection, i.e.,metal-to-metal contact, between the dissimilar metals.

One section was stood upright on its bottom edge in a shallow pool ofwater and held in this position for about 48 hours to wet the paperlayer exposed along the bottom edge of the section. The other sectionwas allowed to lay on a bench at room temperature for the same 48-hourperiod. When the 48- hour period had elapsed the section standing inwater was removed from the water and checked for corrosion. At the sametime the laminate section not contacted with water was checked forcorrosion. For the section contacted with water it was noted that boththe magnesium layer and the aluminum layer had substantiallydeteriorated. With regard to the section not contacted with water, novisible evidence of corrosion could be detected thereon.

EXAMPLE 11 A sheet of paper towel about 7 in. wide and 5 in. long wassoaked in a saturated aqueous solution of sodium chloride. After beingthoroughly soaked the paper sheet was removed from the solution and thesalt allowed to dry on the paper at room temperature. To one side of thepaper sheet was adhered a sheet of magnesium-based alloy (AZ61A), whichmeasured about 7 in. wide, 5 in. long and 0.003 in. thick. A sheet ofaluminum foil about 7 in. wide, 5 in. long and 0.002 in. thick wasadhered to the opposite side of the paper sheet, to complete thethree-layer laminate. The laminate was divided into two separatesections measuring about 3.5 in. wide and 5 in. long. Each of the flatlaminate sections was formed into a cylindrical section having a sideseam joint similar to the cylindrical laminate illustrated in FIG. 2, toprovide electronic contact between the metal layers.

Following the procedure of example I, one of the cylindrical sectionswas stood upright in a pool of shallow water and held in this positionfor about 24 hours to wet the exposed paper layer along the bottom ofthe laminate structure. For the same 24-hour period, the othercylindrical laminate was allowed to lay on a bench at room temperature.After 24 hours the section standing in water was removed and checked fordeterioration. It was observed that about half of the magnesium layerand about the same amount of the aluminum layer had been consumed bycorrosion. No corrosion was visible on the cylindrical section which hadlain on the bench.

EXAMPLE 111 Two sheets of paper towel about 4 in. square were soaked ina saturated aqueous solution of sodium chloride and the papers wereallowed to dry at room temperature. The paper sheets were adhered toopposite sides of a sheet of magnesium-based alloy (A261) about 4 in.square and 0.003 in. thick. A sheet of aluminum foil measuring about 4sq. in. by 0.002 in. thick was then adhered to the exposed surface ofeach paper sheet (the surface not adhered to the magnesium layer), tocomplete the five-layer laminate. The top edge of the metal layers,which extended slightly beyond the edge of the paper layers, were foldedover and crimped together to provide electronic contact between themetal layers. The laminate was then cut into two sections of about equalsize, the cut being made through the folded edge so that each sectionhad one edge in which the metal layers were electronically connected.

Following the procedure of example 1, one of the laminate sections wasstood upright in a pool of shallow water and held in this position forabout 48 hours. For the same 48-hour period the other laminate sectionwas allowed to lay on a bench at room temperature. After 48 hours thesection which had been standing in water was removed and checked forcorrosion. It was observed that about half of each of the metal layershad been consumed from corrosion. With regard to the laminate sectionnot contacted with water, no visible evidence of corrosion could beobserved.

What is claimed is:

1. A metal container having at least one wall member comprising astructural laminate including:

a. at least one layer of an aluminum-based metal;

b. at least one layer of a metal anodic to the aluminumbased metal, thesaid metal layers being electronically connected; and

c. at least one layer of an electrolyte-forming composition containingan alkali metal or an alkaline earth metal salt, the electrolyte-formingcomposition being positioned between the metal layers and being capable,when contacted with moisture, of ionizing to provide ionic communicationbetween the metal layers.

2. The container of claim 1 which includes means integral with thelaminate structure for severing a portion of the laminate.

3. The container of claim 1 in which the aluminum-based metal layer isan alloy containing aluminum and iron and the anodic metal layer is amagnesium-based alloy.

4. The container of claim 1 in which the electrolyte-forming compositionis an anhydrous alkali metal salt of a strong acid.

5. The container of claim 1 in which the electrolyte-forming compositionis impregnated into a strip of bibulous material.

6. The container of claim 1 wherein the electrolyte-forming compositioncontains a hygroscopic additive.

7. The container of claim 6 wherein the hygroscopic additive is calciumchloride or magnesium chloride.

8. The container of claim 1 in which the anodic metal layer is amagnesium-based alloy and the electrolyte-forming composition is sodiumchloride.

9. The container of claim 1 in which the electrolyte-forming compositionis sealed between the said metal layers.

10. The container of claim 1 in which the total thickness of thecontainer laminate is not more than 0.250 inch.

ll. A metal container having at least one sidewall member, a top wallmember and a bottom wall member, wherein the respective wall memberscomprise a structural laminate including:

a. at least one layer of an aluminum-based metal;

b. at least one layer of a metal anodic to the aluminum based metal, thesaid metal layers of each wall member being electronically connected;and

. at least one layer of an electrolyte-forming composition containing analkali metal or an alkaline earth metal salt, the electrolyte-formingcomposition being positioned between the metal layers and being capable,when contacted with moisture, of ionizing to provide ionic communicationbetween the metal layers.

12. The container of claim 11 which includes a chime portion formed bythe juncture of the top wall member and bottom wall member with thesidewall member, wherein adjacent metal layers in the said chimeportions have at least one perforation therethrough to enhance moisturecommunication between the said top wall member and sidewall member andthe said bottom wall member and sidewall member.

UNITED STATES PATENT OFFICE -CERTIFICATE OF COEiRECTION Patent No. 3, 9,91 Dated 21 December 1971 Inventor(s) rcy F- George It is certified that"error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

In column 2, line 16, delete "AZ61A," and insert may line 32, delete"(l5)" and insert are Signed and sealed this 13th day of June 1972.

(SEAL) Attest':

EDWARD M.FLETCHER ,JR I ROBERT GOI'TSCHALK Attesting OfficerCommissioner of Patents

2. The container of claim 1 which includes means integral with thelaminate structure for severing a portion of the laminate.
 3. Thecontainer of claim 1 in which the aluminum-based metal layer is an alloycontaining aluminum and iron and the anodic metal layer is amagnesium-based alloy.
 4. The container of claim 1 in which theelectrolyte-forming composition is an anhydrous alkali metal salt of astrong acid.
 5. The container of claim 1 in which theelectrolyte-forming composition is impregnated into a strip of bibulousmaterial.
 6. The container of claim 1 wherein the electrolyte-formingcomposition contains a hygroscopic additive.
 7. The container of claim 6wherein the hygroscopic additive is calcium chloride or magnesiumchloride.
 8. The container of claim 1 in which the anodic metal layer isa magnesium-based alloy and the electrolyte-forming compositioN issodium chloride.
 9. The container of claim 1 in which theelectrolyte-forming composition is sealed between the said metal layers.10. The container of claim 1 in which the total thickness of thecontainer laminate is not more than 0.250 inch.
 11. A metal containerhaving at least one sidewall member, a top wall member and a bottom wallmember, wherein the respective wall members comprise a structurallaminate including: a. at least one layer of an aluminum-based metal; b.at least one layer of a metal anodic to the aluminum-based metal, thesaid metal layers of each wall member being electronically connected;and c. at least one layer of an electrolyte-forming compositioncontaining an alkali metal or an alkaline earth metal salt, theelectrolyte-forming composition being positioned between the metallayers and being capable, when contacted with moisture, of ionizing toprovide ionic communication between the metal layers.
 12. The containerof claim 11 which includes a chime portion formed by the juncture of thetop wall member and bottom wall member with the sidewall member, whereinadjacent metal layers in the said chime portions have at least oneperforation therethrough to enhance moisture communication between thesaid top wall member and sidewall member and the said bottom wall memberand sidewall member.